Novel fluorocopolymers for the hydrophobic and oleophobic treatment of various substrates

ABSTRACT

Fluorocopolymers resulting from the polymerization of a polyfluoromonomer, of an aminoalcohol (meth)acrylate and of methacrylic acid in a distillable organic solvent, and aqueous compositions containing them.

DESCRIPTION

[0001] The subject of the present invention is novel fluorocopolymersand their use for the coating and the impregnation of varioussubstrates, such as textiles, leather, wood, non-wovens, metal,concrete, stone and, more particularly, paper and similar articles, forthe purpose of making them oleophobic and hydrophobic. The inventionalso relates to the substrates thus treated.

[0002] To achieve this objective, many fluoroderivatives have alreadybeen proposed.

[0003] International Application WO 98/23657 thus teaches cationicfluorocopolymers capable of being obtained by the copolymerization of:

[0004] 52 to 92% by weight of one or more polyfluoromonomers of generalformula:

[0005] in which Rf represents a perfluorinated radical, having astraight or branched chain, containing 2 to 20 carbon atoms, preferably4 to 16 carbon atoms, B represents a divalent linking which is linked toO by a carbon atom and which may comprise one or more oxygen, sulphurand/or nitrogen atoms, one of the symbols R represents a hydrogen atomand the other a hydrogen atom or an alkyl radical containing 1 to 4carbon atoms;

[0006] 1 to 25% of one or more monomers of general formula:

[0007] in which B′ represents a linear or branched alkylene radicalcontaining 1 to 4 carbon atoms, R′ represents a hydrogen atom or analkyl radical containing 1 to 4 carbon atoms, the symbols R¹ and R²,which are identical or different, each represent a hydrogen atom, alinear or branched alkyl radical containing 1 to 18 carbon atoms or ahydroxyethyl or benzyl radical, or R¹ and R² together with the nitrogenatom to which they are linked form a morpholino, piperidino orpyrrolidin-1-yl radical;

[0008] 1 to 25% of a vinyl derivative of general formula:

R″—CH=CH₂

[0009] in which R″ may be an alkyl carboxylate or alkyl ether groupcontaining from 1 to 18 carbon atoms.

[0010] The copolymerization reaction leading to the fluorocopolymersdescribed by that international application is carried out in solutionin a water-miscible organic solvent or solvent mixture and is followedby a step of dilution with an aqueous solution of a mineral or organicacid. This dilution step is carried out in the presence of hydrogenperoxide or is followed by a treatment by means of an aqueous hydrogenperoxide solution.

[0011] After the said dilution step, it is necessary to carry out avacuum distillation or to flush with an inert gas, for example nitrogen,in order to remove the volatile compounds and to obtain a compositionthat can be sold and applied to the substrate to be treated.

[0012] The solvents exemplified in that application are, mostly,mixtures based on N-methylpyrrolidone. Because of their boiling point,these solvents are not completely removed by the distillation operationso that significant quantities of them remain in the commercialcomposition.

[0013] This commercial composition is thus in the form of a solution,thereby giving it stability properties which are highly advantageous forits transportation and its storage.

[0014] However, for some applications, and especially for the treatmentof papers or similar articles intended for the field of packaging foodproducts, it is desirable to reduce the amount of any solvents incommercial compositions, or even to completely eliminate them therefrom.

[0015] International Application WO 98/23657 mentions (cf. page 5 lines14-15) that the use of light solvents makes it possible to obtain, afterdistillation, a commercial composition containing no organic solvent.

[0016] However, during the operation of distilling these light solvents,a gradual precipitation of the cationic fluorocopolymers occurs, whichthen results in an unstable aqueous dispersion, i.e. one which resultsin a settling in a few hours. Such a dispersion is unsuitable as acommercializable composition.

[0017] It has now been found that the introduction of an anionicmonomer, or a monomer which is potentially anionic by varying the pH,into the copolymers described by the international application, and amodification to their synthesis process, makes it possible to obtainnovel fluorocopolymers which confer on various substrates, andespecially on paper, the same hydrophobic and oleophobic properties andwhich, in addition, may be in the form of aqueous compositions whichcontain no organic solvents and are stable over time.

[0018] Fluorocopolymers according to the present invention are obtainedby polymerization of a monomer mixture comprising by weight:

[0019] (a) from 50 to 92%, preferably from 70 to 90%, of one or morepolyfluoromonomers of general formula:

[0020] in which:

[0021] Rf represents a perfluorinated radical having a straight orbranched chain, containing 2 to 20 carbon atoms, preferably 4 to 16carbon atoms,

[0022] B represents a divalent linking which is linked to O by a carbonatom and which may comprise one or more oxygen, sulphur and/or nitrogenatoms,

[0023] one of the symbols R represents a hydrogen atom and the other ahydrogen atom or an alkyl radical containing 1 to 4 carbon atoms;

[0024] (b) from 1 to 25%, preferably from 8 to 18%, of one or moremonomers of general formula:

[0025] in which:

[0026] B′ represents a linear or branched alkylene radical containing 1to 4 carbon atoms,

[0027] R′ represents a hydrogen atom or an alkyl radical containing 1 to4 carbon atoms,

[0028] the symbols R¹ and R², which are identical or different, eachrepresent a hydrogen atom, a linear or branched alkyl radical containing1 to 18 carbon atoms or a hydroxyethyl or benzyl radical, or R¹ and R²together with the nitrogen atom to which they are linked form amorpholino, piperidino or pyrrolidin-1-yl radical;

[0029] (c) from 0.5 to 20%, preferably from 1 to 10%, of an anionicmonomer or a monomer which is potentially anionic by varying the pH(III), such as alkene carboxylic acids, monoolefinic derivatives ofsulphonic acid, and their salts of alkali or alkaline-earth metals;

[0030] (d) from 2 to 10% of a vinyl derivative of general formula:

R″—CH=CH₂  (IV)

[0031] in which R″ may be an alkyl carboxylate or alkyl ether groupcontaining from 1 to 18 carbon atoms;

[0032] (e) from 0 to 10%, preferably from 0 to 8%, of any monomer otherthan the monomers of formulae I, II, III and IV;

[0033] With regard to monomer (c), mention may be made especially of(meth)acrylic acid as an example of an alkene carboxylic acid andacrylamidomethyl-propanesulphonic acid as an example of a monoolefinicderivative of sulphonic acid.

[0034] The fluorocopolymers according to the present invention areprepared by copolymerization of the monomers in solution in adistillable organic solvent. The term “distillable” solvent isunderstood to mean any organic solvent or solvent mixture whose boilingpoint at atmospheric pressure is less than 150° C. Next, the reactionmixture is diluted with water in the presence of a mineral or organicacid in order to salify the macromolecules.

[0035] According to a preferred variant of the invention, this dilutionstep is carried out in the presence of hydrogen peroxide or is followedby a treatment by means of an aqueous hydrogen peroxide solution.

[0036] These fluorocopolymers can be applied to various substrates, suchas leather, non-wovens, building materials, paper and board. Inparticular, they can be applied to paper using various techniques(applied in a size press or applied in the bulk), thus giving the paper,without the need for additives (sequestrants, retention agents, fixingresins, etc.), excellent hydrophobic and oleophobic properties.

[0037] According to the present invention, it is preferred to use:

[0038] (a) as polyfluoromonomers of formula I, the compounds of formula:

[0039] in which R_(F) is a perfluoroalkyl radical containing 4 to 16carbon atoms;

[0040] (b) dimethylaminoethyl methacrylate or N-tert-butylaminoethylmethacrylate as monomer of formula II;

[0041] (c) methacrylic acid as monomer of formula III; and

[0042] (d) vinyl acetate as monomer of formula IV.

[0043] As distillable organic solvent in which the copolymerization iscarried out, mention may be made by way of non-limiting example ofketones (for example acetone or methyl ethyl ketone), of alcohols (forexample isopropanol) and of ethers (for example THF or dioxane).

[0044] For implementing the invention, it is preferred to use, assolvent, methyl isobutyl ketone (MIBK) or methyl ethyl ketone (MEK) or amixture of these with acetone.

[0045] The total concentration of monomers in the organic solvent orsolvent mixture may range from 20 to 70% by weight and is preferablybetween 40 and 60%.

[0046] The copolymerization is carried out in the presence of at leastone initiator, used in an amount from 0.1 to 2% with respect to thetotal weight of monomers. As initiators, it is possible to use peroxidessuch as benzoyl peroxide, lauroyl peroxide, succinyl peroxide andtert-butyl perpivalate, or azo compounds such as, for example,2,2′-azobis(isobutyronitrile), 4,4,′-azobis(4-cyanopentanoic acid). Thecopolymerization step may be carried out at a temperature ranging from40° C. up to the boiling point of the reaction mixture. It is preferablycarried out at between 60 and 90° C.

[0047] The dilution step consists in adding an aqueous solution of astrong or moderately strong mineral or organic acid, that is to say anacid whose dissociation constant or whose first dissociation constant isgreater than 10⁻⁵, to the organic solution of the copolymer.

[0048] As examples of such acids, mention may be made of hydrochloric,hydrobromic, sulphuric, nitric, phosphoric, acetic, formic, propionicand lactic acids, but it is preferred to use acetic acid. The amount ofaqueous solution to be used and its acid concentration must besufficient, on the one hand, to completely salify the amine functionalgroups provided by the monomer(s) of formula II and, on the other hand,to obtain a final copolymer solution having a solids content of between5 and 30%, preferably between 20 and 30%. In order to completely salifythe amine functional groups, the amount of acid is advantageouslybetween 0 and 5 acid equivalents, preferably between 1 and 2equivalents, with respect to the monomer(s) of formula II.

[0049] The amount of hydrogen peroxide used is between 0 and 10%,preferably between 0.5 and 4%, with respect to the total initial weightof monomers. The treatment is carried out at between 25 and 100° C.,preferably at between 70 and 85° C.

[0050] The subject of the present invention is also the aqueouscompositions comprising a fluorocopolymer as defined above. The saidcompositions are obtained by completing the process for manufacturingthe fluorocopolymer as defined above with a distillation step, so as toremove any trace of organic synthesis solvent. The aqueous compositionsobtained therefore do not have a flashpoint between 0 and 100° C.according to the ASTM D3828 standard. The distillation may be carriedout at atmospheric pressure or reduced pressure. In general, theseaqueous compositions are in the form of dispersions which are stableover time. Thus, these dispersions remain homogeneous and can thereforebe transported and stored while still remaining capable of being usedfor the hydrophobic and oleophobic treatment of substrates.Advantageously, they are also water-dilutable.

[0051] The concentration of fluorocopolymer according to the inventionin water is generally between 1 and 50%, preferably between 20 and 30%.

[0052] The subject of the present invention is also a solid substratecomprising at least one fluorocopolymer according to the invention, asdefined above.

[0053] As substrates capable of being made oleophobic and hydrophobicwith the products according to the invention, it is preferred to usepaper, board and similar materials. It is also possible to use otherhighly varied materials such as, for example, woven or non-wovenarticles based on cellulose or regenerated cellulose, on natural,artificial or synthetic fibres such as cotton, cellulose acetate, wool,silk, polyamide, polyester, polyolefin, polyurethane orpolyacrylonitrile fibres, leather, plastics, glass, wood, metals,porcelain and painted surfaces. It may also be advantageous to treatbuilding materials such as concrete, stone, brick and tiles with theproducts according to the invention.

[0054] The aqueous compositions comprising a fluorocopolymer accordingto the invention are mainly applied diluted in an aqueous medium usingknown techniques, for example by coating, impregnation, immersion,spraying, brushing, padding or film-coating.

[0055] The products according to the invention can be applied in aqueoussolution to paper, either onto the surface of the already completedsubstrate (preferably in an amount of 0.05 to 0.2% fluorine with respectto the weight of paper) or into the body of the material, that is to sayinto the paper pulp (preferably in an amount of 0.2 to 0.4% fluorinewith respect to the weight of pulp).

[0056] The substrates thus treated exhibit good oleophobic andhyrophobic properties after simple drying at room temperature or at hightemperature, optionally followed by a heat treatment which can range,depending on the nature of the substrate, up to 200° C.

[0057] To obtain good attachment of the fluorocopolymers according tothe invention to the substrates to which they have been applied, and, inaddition, to confer a specific effect, it is sometimes advantageous tocombine them with certain additives, polymers, thermocondensableproducts and catalysts capable of promoting their crosslinking with thesubstrate. Mention may be made, as such, of urea-formaldehyde ormelamine-formaldehyde condensates or precondensates, epoxy derivates,such as diglycidylglycerol, polyamine-epichlorohydrin resins, glyoxaland its derivates, polyvinyl alcohols and cationic, oxidized andamphoteric starches.

[0058] It may also be advantageous to combine the fluorocopolymersaccording to the invention with one or more nonionic and/or cationicsurfactants in order to improve the wetting of the substrate. The weightof this or these surfactants with respect to the total weight ofcopolymer may vary from 0 to 100%.

[0059] The surfactants may be added to the organic solution during thecopolymerization reaction, during the dilution or to the aqueouscomposition obtained after distilling off the solvent. They may also beadded at the time of application of the copolymers according to theinvention.

[0060] The following tests were used to evaluate the performance of thetreated substrates according to the invention:

Greaseproofness test or “kit value”

[0061] This test, described in TAPPI, Vol. 50, No. 10, pages 152A and153A and in the RC338 and UM511 standards, makes it possible to measurethe greaseproofness of substrates using mixtures of castor oil, tolueneand heptane. These mixtures contain variable amounts of these threeproducts: Kit Number Volume of Volume of Volume of (Kit Value) castoroil toluene heptane 1 200  0  0 2 180 10 10 3 160 20 20 4 140 30 30 5120 40 40 6 100 50 50 7  80 60 60 8  60 70 70 9  40 80 80 10   20 90 9011   0 100  100  12   0 90 110 

[0062] The test consists in gently depositing drops of these mixtures onthe treated paper. The drops are left on the paper for 15 seconds andthen the appearance of the paper or board is carefully observed and thewetting or penetration revealed by a browning of the surface isrecorded. The number corresponding to the mixture containing the highestpercentage of heptane, which does not penetrate or wet the paper, is the“kit value” of the paper and is regarded as being the degree ofoleophobicity of the treated paper. The higher the “kit value”, thebetter the oleophobicity of the paper.

Cobb Test

[0063] The Cobb test [NF EN 20535-ISO 535 (1994)] consists in measuringthe weight (in g) of water absorbed during one minute by a square meterof paper supporting a water height of one centimeter.

Test of resistance to dry animal food

[0064] 200 g of dry dog food, of the ROYAL CANIN (ST 35 grade) brand,are deposited on a 100 cm² area of treated paper in acontrolled-environment oven at 60° C. and 65% relative humidity.

[0065] The assembly is placed on an untreated absorbent paper (filterpaper type) of the same area. After this, a 3.5 kg weight is placed onthe entire assembly, which is left in the oven for 3 days.

[0066] The diffusion of the fats is evaluated by measuring the totalarea of the stains which have appeared on the absorbent paper. It isconsidered that the barrier to the fats is effective when the stainedarea is less than 10% of the total area of the absorbent paper. Thisvalue is called the percentage soak-through.

Oleophobicity Test

[0067] The oleophobicity was measured on certain substrates using themethod described in “AATCC Technical Manual”, Test Method 118-1992,which evaluates the non-wettability of the substrate using a series ofoily liquids numbered 1 to 8:

[0068] No. 1: liquid paraffin

[0069] No. 2: liquid paraffin/n-hexadecane (64/35)

[0070] No. 3: n-hexadecane

[0071] No. 4: n-tetradecane

[0072] No. 5: n-dodecane

[0073] No. 6: n-decane

[0074] No. 7: n-octane

[0075] No. 8: n-heptane.

[0076] The test consists in depositing drops of these mixtures on thetreated substrates and then in observing the effect of the drop after 30seconds of contact. The rating is given by the number of the last dropof liquid which has neither penetrated nor wetted the substrate.

Hydrophobicity Test

[0077] The method is adapted from the oleophobicity test. The testliquids numbered 1 to 10 are mixtures by weight of demineralized waterand 2 propanol. Composition by weight Test liquid Demineralizedreference numbers water 2-Propanol 1 90 10 2 80 20 3 70 30 4 60 40 5 5050 6 40 60 7 30 70 8 20 80 9 10 90 10   0 100 

[0078] The test consists in depositing drops of these mixtures on thetreated substrates and then in observing the effect of the drop after 30seconds of contact. The rating is given by the number of the last dropof liquid which has neither penetrated nor wetted the substrate.

[0079] The following examples illustrate the invention without limitingit. Unless otherwise mentioned, the parts indicated are parts by weight.

EXAMPLE 1

[0080] A reactor of 600 parts by volume, fitted with a stirrer, athermometer, a reflux condenser, a dropping funnel, a nitrogen inlet anda heater, is charged with 40 parts of MIBK, 2 parts of MEK, 27 parts ofacetone, 16 parts of dimethylaminoethyl methacrylate, 8.8 parts of vinylacetate, 1.2 parts of methacrylic acid, 81.4 parts of a mixture offluoracrylates of formula:

[0081] where n is equal to 5, 7, 9, 11 and 13 in mean and respectiveweight ratios of 1/63/25/9/3, and 0.4 part of 4,4′-azobis(4-cyanopentanoic acid).

[0082] The mixture is heated at 70° C. under a nitrogen atmosphere for4.5 hours, then the temperature is raised to 78° C. 0.5 hours later,0.32 part of 4,4′-azobis(4-cyanopentanoic acid) is added and the reactoris left at 78° C. for 3 hours.

[0083] Next, an aqueous solution comprising 290 parts of water, 8 partsof acetic acid and 2.5 parts of 35 wt % hydrogen peroxide is poured inat 70° C.

[0084] The mixture is held for two hours at 70° C. under a stream ofnitrogen and then the solution is distilled at a reduced pressure so asto obtain a 25% solution of fluorocopolymer according to the invention.

[0085] The mixture is then cooled down to room temperature. 410 parts ofan amber-coloured dispersion (S1) are thus obtained, this dispersionbeing completely stable over time.

[0086] This dispersion does not include an organic solvent and thereforedoes not have a flashpoint between 0 and 100° C. according to ASTM D3828standard.

COMPARATIVE EXAMPLE 1

[0087] The procedure is as in Example 1 but with the methacrylic acidbeing completely omitted and replaced, weight for weight, with vinylacetate.

[0088] 410 parts of an amber-coloured dispersion (Sc1) comprising afluorocopolymer according to International Application WO 98/23657 arethen obtained. This dispersion settles after a few hours.

EXAMPLE 2

[0089] The procedure is as in Example 1 but with 1.8 parts ofmethacrylic acid being added to the detriment, weight by weight, of thevinyl acetate, i.e. 3 parts of methacrylic acid and 7 parts of vinylacetate.

[0090] 410 parts of a completely stable solvent-free amber-coloureddispersion (S2), containing 25% of fluorocopolymer according to theinvention, are then obtained.

COMPARATIVE EXAMPLE 2

[0091] The procedure is as in Example 2 but, on the one hand, with theMIBK/MEK/acetone solvent mixture being replaced with 90 parts of NMP and10 parts of acetone and, on the other hand, with only 200 parts of waterbeing used for the dilution.

[0092] 410 parts of a very stable amber-coloured solution (Sc2) is thenobtained, but this still contains an amount of NMP greater than 20%.

EXAMPLE 3

[0093] The solutions (S1), (Sc1), (S2), and (Sc2) are used.

[0094] The size-press ponds described in the table below are preparedwith these various constituents. Constituents Pond number of the pond(g/l) 1 2 3 4 Solution S1 15 Solution Sc1 15 Solution S2 15 Solution Sc215 Water 985 985 985 985 Total 1000 1000 1000 1000

[0095] The pH of the ponds is set to 6.5. The various compositions areapplied in a size press to a 70 g/m² paper composed of unsized bleachedpulp. The degree of absorption of the pond by the paper (known in theart by the name “degree of application”) is about 80%. After drying forone minute at 120° C., the paper thus treated is stored for 1 day atroom temperature and then subjected to the various tests.

[0096] The results obtained are combined in the following table: Papertreated with pond No. Untreated Tests 1 2 3 4 paper Kit value 12 10 1112  0 Cobb (g/m²) 19 20 19 21 >100  Soak-through (%)  0 100   0  0 100

[0097] Comparing the results obtained on papers 1 and 3 on the one handand paper 4 on the other, shows that the performance of thefluorocopolymers in the form of aqueous compositions, according to theinvention, are comparable to those of the fluorocopolymers ofInternational Application WO 98/23657 in the form of a solutioncontaining an organic solvent.

[0098] In addition, comparing the results obtained on papers 1 and 3 onthe one hand and paper 2 on the other, shows that introducingmethacrylic acid as monomer makes it possible to achieve a substantiallyimproved grease barrier effect.

EXAMPLE 4

[0099] Solutions (S1) and (Sc2) are also used.

[0100] 20 g of deciduous bleached kraft pulp, refined to 25° SR, aredispersed in 2.4 l of water for 45 minutes, the pH being adjusted to 6.5with H₂SO₄. Next, 0.6 g of solution is added to this preparation, whilestirring. All this is separated into 9 fractions of 270 g. Each fractionis diluted with 2 l of water, while stirring, in a bowl of a FRANKapparatus and filtered under vacuum in order to obtain a handsheet.Finally, the handsheet is dried under vacuum for 5 minutes at 90° C. onthe plates of the FRANK apparatus. The characteristics of the papersheets thus bult-treated with each solution are given in the tablebelow: Handsheet made from pulp example Untreated Tests S1 Sc2 handsheetKit value 12 12   0 Cobb (g/m²) 19 20 >100

[0101] Comparing the results obtained on the handsheets made from pulpsS1 and Sc2 shows that the performance of the fluorocopolymer in the formof an aqueous composition, according to the invention, is comparable tothat of the fluorocopolymer of International Application WO 98/23657 inthe form of a solution containing an organic solvent.

EXAMPLE 5

[0102] Solutions (S1) and (Sc2) are also used. Each solution is dilutedwith water, at room temperature, so as to obtain an aqueous solutioncontaining 2% fluorocopolymer.

[0103] This solution is then sprayed in the form of a cross ontospecimens of lambskin leather using a Volumair T21 sprayer. The amountdeposited is on average 150 g/m². After drying for 24 hours at roomtemperature, the leathers are tested.

[0104] Their characteristics are given in the table below: Lambskintreated with Tests (S1) (Sc2) Control Oleophobicity test 4 4 0Hydrophobicity test 8 5 0

[0105] This table shows the remarkable effectiveness of the products forgiving leather good water-repellency and oil-repellency properties. Thefluorocopolymer according to the invention in the form of an aqueousdispersion (S1) has superior properties to the fluorocopolymer ofApplication WO 98/23657 in the form of a solution (Sc2) containing anorganic solvent.

EXAMPLE 6

[0106] The procedure is exactly as in Example 5 for treating a polyamidefabric with (S1).

[0107] The results are expressed in the following table: Polyamidetreated with Tests (S1) Control Oleophobicity test 4 0 Hydrophobicitytest 8 0

[0108] This table shows the remarkable effectiveness of the product toprovide water-repellency and oil-repellency properties on a textile.

[0109] Although the invention has been described in conjunction withspecific embodiments, it is evident that many alternatives andvariations will be apparent to those skilled in the art in light of theforegoing description. Accordingly, the invention is intended to embraceall of the alternatives and variations that fall within the spirit andscope of the appended claims. The foregoing reference is herebyincorporated by reference.

1. Fluorocopolymers capable of being obtained by polymerization of amonomer mixture comprising by weight: (a) from 50 to 92%, preferablyfrom 70 to 90%, of one or more polyfluoromonomers of general formula:

 in which: Rf represents a perfluorinated radical having a straight orbranched chain, containing 2 to 20 carbon atoms, preferably 4 to 16carbon atoms, B represents a divalent linking which is linked to O by acarbon atom and which may comprise one or more oxygen, sulphur and/ornitrogen atoms, one of the symbols R represents a hydrogen atom and theother a hydrogen atom or an alkyl radical containing 1 to 4 carbonatoms; (b) from 1 to 25%, preferably from 8 to 18%, of one or moremonomers of general formula:

 in which: B′ represents a linear or branched alkylene radicalcontaining 1 to 4 carbon atoms, R′ represents a hydrogen atom or analkyl radical containing 1 to 4 carbon atoms, the symbols R¹ and R²,which are identical or different, each represent a hydrogen atom, alinear or branched alkyl radical containing 1 to 18 carbon atoms or ahydroxyethyl or benzyl radical, or R¹ and R² together with the nitrogenatom to which they are linked form a morpholino, piperidino orpyrrolidin-1-yl radical; (c) from 0.5 to 20% preferably from 1 to 10%,of an anionic monomer or a monomer which is potentially anionic byvarying the pH (III), such as alkene carboxylic acids, monoolefinicderivatives of sulphonic acid, and their salts of alkali oralkaline-earth metals; (d) from 2 to 10% of a vinyl derivative ofgeneral formula: R″—CH=CH₂  (IV)  in which R″ may be an alkylcarboxylate or alkyl ether group containing from 1 to 18 carbon atoms;(e) from 0 to 10%, preferably from 0 to 8%, of any monomer other thanthe monomers of formulae I, II, III and IV; the said copolymerizationcomprising: the dissolving of the monomers in a distillable organicsolvent; and then the diluting of the reaction mixture with water in thepresence of a mineral or organic acid in order to salify themacromolecules.
 2. Fluorocopolymers according to claim 1 , characterizedin that the diluting with water is carried out in the presence ofhydrogen peroxide or is followed by a treatment by means of an aqueoushydrogen peroxide solution.
 3. Fluorocopolymers according to either ofclaims 1 and 2, characterized in that the following are used: (a) aspolyfluoromonomers of formula I, the compounds of formula:

 in which R_(F) is a perfluoroalkyl radical containing 4 to 16 carbonatoms; (b) dimethylaminoethyl methacrylate or N-tert-butylaminoethylmethacrylate as monomer of formula II; (c) methacrylic acid as monomerof formula III; and (d) vinyl acetate as monomer of formula IV. 4.Fluorocopolymers according to one of claims 1 to 3 , characterized inthat methyl isobutyl ketone (MIBK) or methyl ethyl ketone (MEK), or amixture of these with acetone, is used as the organic solvent. 5.Fluorocopolymers according to one of claims 2 to 4 , characterized inthat the amount of hydrogen peroxide used is between 0 and 10%,preferably between 0.5 and 4%, with respect to the total initial weightof monomers.
 6. Aqueous compositions comprising from 1 to 50%,preferably from 20 to 30%, of a fluorocopolymer as defined in one ofclaims 1 to 5 .
 7. Solid substrate comprising at least onefluorocopolymer as defined in one of claims 1 to 5 .
 8. Solid substrateaccording to claim 7 , characterized in that it is paper or board.